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Why we use 330 ohm resistor to connect a LED?
Possible Duplicate:
Correct formula for LED current-limiting resistor?
Why we use 330 ohm resistor to connect a LED ?
I mean:
the R is by practice 330 ohm.
Why this value? How do I calculate it? what's the purpose of it?
Is there a specific…
xsari3x
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25
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5 answers
Help learning from a mistake connecting an oscilloscope
I have built this circuit to dim a lamp with a PWM signal. It had an issue where the MOSFET was getting really hot. So I wanted to know what was happening on the gate of the MOSFET.
I turned the PWM signal off and with my multimeter I measured…
cyrili101
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25
votes
14 answers
How to clean a potentiometer?
I have a couple of potentiometers that haven't been touched in quite some time. In fact, probably not in 15 years. So now they produce noisy output, presumably from oxides or some other crud that has built up on the contact surfaces.
Outright…
JustJeff
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25
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7 answers
What will happen if the output from a NOT-gate injected- BACK to its OWN input?
Not-gate, if get a 0(Off) input, it gives an 1 (On) output. And if get a 1 (On) input, gives-back a 0(Off) output.
Now, if-I could bring the output back to the input of the not-gate, then what will happen? If the gate is getting a 1 input, it is…
Always Confused
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25
votes
4 answers
Are Common Mode Choke Coils needed on USB?
I was looking over the schematic for the GumStix Palo 43 and noticed they used a common mode choke coil on the data lines coming in from USB.
I understand how this design can help remove noise coming in on the USB lines, but I wonder if it is…
Kellenjb
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25
votes
1 answer
Does anyone know the history of the earth ground symbol
I Googled for hours, asked every EE professor in my college, then checked every electrical engineering book in my university's library (hours), and have found nothing about the history of the ground symbol. Please point me if you can.
Who coined…
Dave Sims
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25
votes
6 answers
Why are Atmel AVRs so popular?
A recent question asked about the advantages/disadvantages of various types of MCU. AVRs seemed not even worth a mention given the answers. Why then does it seem to an outsider that AVRs are experiencing a rush of popularity? Is this solely due to…
Tim
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25
votes
8 answers
What are the advantages of using FPGAs over TTL in intro computer architecture?
I teach the one and only computer architecture course at a liberal arts college. The course is required for the computer science major and minor. We do not have computer engineering, electrical engineering, other hardware courses, etc. My primary…
Ellen Spertus
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25
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4 answers
Yogurt on a PID controller
How do you change the tuning of a PID controller to deal with changing thermal properties?
The project: I am making yogurt. It cultures at 110 deg F for about half a day; you put in milk and a little starter culture and get yogurt. Save a little for…
hildred
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25
votes
4 answers
Reliability problems with an array of 91 high-power LEDs
I have designed and printed a 4-layer PCB that accommodates 91 infrared LEDs in a 7x13 rectangular layout. This will be used as a backlight for a machine vision project. I am having a problem where individual LEDs are burning out or perhaps becoming…
cxrodgers
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25
votes
4 answers
After PCB layout
After you've designed your circuit and have the PCB layout completed, how do people in the EE industry go about designing the enclosure? What kind of considerations need to be made to accommodate the PCB in an enclosure?
inbinder
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25
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3 answers
STM32F4 and HAL
So I've been experimenting a while with the STM32F407 (I'm new to ARM) and decided to write a simple app using the HAL libraries since it seems ST has discontinued the Standard Peripherals Libraries.
So my question is, what is the point in HAL?…
John
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25
votes
4 answers
Why do CPU's typically connect to only one bus?
I found a motherboard architecture here:
This looks to be the typical layout of motherboards. EDIT: Well, apparently it's not so typical anymore.
Why does the CPU connect to only 1 bus? That front-side bus looks like a major bottleneck. Wouldn't it…
DrZ214
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25
votes
6 answers
Why are NAND Gates cheap?
In my digital electronics labs and lectures we are told to try and make things from NAND gates, because they are the cheapest kind of gate available to buy. Why is this? Why isn't an OR/AND gate the cheapest to buy?
Dean
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25
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9 answers
Is a microwave's output power proportional to the mass of its contents?
My friend and I are having a heated debate.
On the one hand, he thinks that a microwave oven that is empty, consumes almost no power (not considering lights, lcd, etc). He says that once you put an item in the oven, such as a glass of water, the…
Matthew Goulart
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